hps_accel/software_cfu: small optimization
hps_accel/software_cfu: small optimization

A small optimization of the software_cfu. Having tried several obvious
"optimizations" it turned out that all but one was actually a
pessimisation.

This change saves about 3.5s of the two minute evaluation time.

Signed-off-by: Alan Green <97e77871b5fcc4941bebceb4338c97c1fd149f8c@google.com>

google/CFU-Playground,google/CFU-Playground,google/CFU-Playground,google/CFU-Playground